SSL devices generally use semiconductor light emitting diodes (“LEDs”), organic light emitting diodes (“OLEDs”), and/or polymer light emitting diodes (“PLED”) as sources of illumination rather than electrical filaments, a plasma, or a gas. Mobile phones, laptop computers, digital cameras, MP3 players, and other portable electronic devices can utilize SSL devices for background illumination. SSL devices can also be used for signage, indoor lighting, outdoor lighting, and other types of general illumination.
FIG. 1 shows a conventional vertical SSL device 10 including a light emitting structure 17 having a p-type gallium nitride (GaN) 12, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 14, and n-type GaN 16 in series. The SSL device 10 also includes a support substrate 18 and a p-type contact 20 between the support substrate 18 and the p-type GaN material 12. Conventional support substrates 18 are typically sapphire or a semiconductor material having a wafer form factor. The SSL device 10 also includes an n-type contact 22 on top of the SSL device 10 that can be wirebonded to an external contact 24 of an external host device 26. As voltage is applied between the n-type contact 22 and the p-type contact 20, electrical current passes through the light emitting structure 17 and produces light. The SSL device 10 can be made on a wafer that is singulated into individual SSL devices.
Conventional devices use thermo-compression bonding, such as copper-copper (Cu—Cu) bonding, to attach the light emitting structure 17 to the support substrate 18. This process requires high temperatures and pressures that can bow or deform the wafer to the extent that it cracks or warps. Currently LED industry is mostly working with 2-4 inch diameter substrates, which limits the throughput and increases costs because fewer SSL devices can be produced on such small wafers. Even at these diameters warp and bow of the wafers is a problem for fabrication of LEDs. This problem becomes severe for large diameter (>4 inch) wafers.